The Tang is seen as a golden age of Chinese power and culture. The unification of the Sui, for once, lasted for a long time and the dynastic founder Gaozu (born as Li Yuan) managed to achieve a peaceful succession to his son Taizong. Taizong is revered as one of the great emperors of China with a keen intelligence and appetite for hard work.
The capital Changan (near Xian) became one of the first great cities in the World. It covered 30 square miles and had one million people within the walls and about the same number outside. The City was arranged in a grid pattern, each square of the grid was a self contained unit locked at night. China extended its territory to Tibet and Korea. It limited the advance of the Muslim armies from the West and was a period of learning and high art. A new criminal code was instituted and porcelain started production in quantity and fine quality. The open examination system for entry into the civil service was revitalised.
Wu Zetian is the only acknowledged Empress of China in her own right, although it is true that some other emperors were firmly under the control of their wives. Engineering prowess was proven by such feats as an iron chain bridge over the Yellow River at Pujin greatly improving communication in 706AD.
After 750 the power and vitality of the Tang dynasty ebbed away. Attacks from Tibet and Yunnan was a persistent external threat but internal provincial rivalry again weakened government. The powerful and wealthy Buddhist monasteries were suppressed in 845. The imperial eunuchs became more powerful and were the effective rulers in the last years. Eventually internal strife led to fifty years of turmoil with the Five Dynasties period